Understanding the Mysterious World of Two-Source Bonding Wires

Introduction to Two-Source Bonding Wires

Two-source bonding wires refer to a type of wire used to connect semiconductor chips to the pins or leads of integrated circuit (IC) packages. Unlike traditional single-source bonding wires, two-source bonding wires utilize two different wire materials joined together. This allows the wires to benefit from the advantages of both materials.

The main components of a two-source bonding wire are:

The fine wire is generally connected to the chip bond pad, while the coarse wire is connected to the package lead. The joint between the two wires is usually located above the highest loop arc.

Two-source bonding wires offer benefits like:

However, two-source bonding is also more complex compared to traditional single-source bonding. Let's explore the mysterious world of two-source wires in more detail.

The Evolution of Two-Source Bonding Wires

The use of two-source bonding wires evolved over decades of semiconductor and packaging development:

Driving Forces Behind Two-Source Wires

Several factors drove the need for two-source bonding wires:

Two-source bonding provided an innovative solution to balance these conflicting requirements.

How Two-Source Wire Bonding Works

The process of connecting a chip to an IC package with two-source wires involves the following key steps:

  1. Ball bonding - The fine wire section is ball-bonded to the chip bond pad using thermocompression or ultrasonic techniques.

  2. High looping - The wire is looped in an arc up to the required height above the chip.

  3. Coarse wire attachment - The coarse wire is welded onto the fine wire using a laser or electrical discharge.

  4. Stitch bonding - The coarse wire is stitch bonded onto the package lead.

  5. Trimming - The wire is trimmed leaving a small stitch tail.

The joint between the fine and coarse wires is crucial. Parameters like alignment, metallurgical mixing and grain structure affect joint strength and reliability.

Fine Wire Materials Used in Two-Source Bonding

The fine wire carries current from the chip pad and forms the ball bond. Common options include:

The choice of fine wire material depends on factors like:

Trend Towards Copper Fine Wire

Copper is an attractive option for the following reasons:

However, copper oxidation and hardnesses require advanced bonding systems to achieve high yields and reliability. The industry is progressively adopting copper fine wire bonding as the technology matures.

Coarse Wire Selection Criteria and Options

The coarse wire portion must provide the required strength to span from chip to package as well as suit the packaging metallization.

Key selection criteria for the coarse wire include:

Widely used coarse wire options:

The Secret Art of Joining Fine and Coarse Wires

A robust metallurgical joint between the fine and coarse wire sections is critical for wire performance and reliability.

However, joining dissimilar metals like gold and copper or aluminum and copper is tricky:

Common methods for joining the wires include:

Extensive process development and qualification is required to optimize the joint integrity. Parameters like laser energy, pulse duration, discharged voltage profile, wire prep and cleanliness are critical.

I use laser welding for its precision, speed and joint quality. The technique provides the control needed for a reliable two-source bonding process.

Impact of Two-Source Wires on Wire Bonding Tools

Using two-source bonding wires required innovations in wire bonding equipment and tools:

Advanced dual wire bonders allow programming parameters independently for the fine and coarse wire processes. This provides the control and repeatability needed for high-yield two-source bonding.

Features like programmable bond force, ultrasonic power and temperature are optimized for each wire section. Real-time measurements like wire height detection allow responsive process adjustments.

The latest smart bonders ease the challenges of two-source bonding. Their capabilities help unlock the benefits of using hybrid fine-coarse wires.

The Future of Two-Source Wire Bonding

Two-source wire bonding provides an evolving solution to connect chips with increasing I/O density to their packages. Some key trends shaping its future are:

In summary, two-source wire bonding is an advancing technology gaining adoption to reap its benefits while managing the complexity. With diligent engineering and smart equipment, reliable two-source interconnects are within reach.

The mysterious world of hybrid fine-coarse wires is being progressively illuminated to power next-gen semiconductor packages. Through persistent innovation, their full potential can be realized by the industry.